A wave of advertiser defections from prime-time network programs has swept through the television industry in the past two months, and industry executives attribute it primarily to widespread grass-roots objections to sexual themes and explicit language on the public airways.

Unlike movements in the 1970s and early '80s that were led by religious and education groups, the new protests appear to no known organizations but who are increasingly angered by what they see on television.While denying that their standards have slipped, television executives acknowledge there have been lapses into poor taste, some of it a result of cutbacks in censoring. In other cases, they say, audiences have become more conservative and they have been slow to respond to that change. Unlike movements in the 1970s and early '80s that were led by religious and education groups, the new protests appear to be from viewers who belong to no known organizations but who are increasingly angered by what they see on television. In response to letters from angry TV viewers, such major advertisers as Coca-Cola, McDonald's, Chrysler, General Mills, Campbell Soup, Ralston-Purina and Sears have all recently announced cancellations of commercials in television programs because of material cited as offensive in viewer complaints.

Two weeks ago, for example, Ralston-Purina and Domino's Pizza pulled their ads from NBC's long-running comedy show "Saturday Night Live" after complaints about the repetitive use in one sketch of the word penis.

Another NBC series, "Nightingales," has been the subject of protests. Chrysler and Sears withdrew advertising after nursing groups complained that the series portrayed their profession in an unflattering way.

Mennen withdrew in March from ABC's "HeartBeat," a weekly series that is not longer on the air, after complaints from viewers about an episode in which a prostitute had an abortion.

Brandon Tartikoff, the president of entertainment for NBC, the target of many of the protests, said: "I believe there are some changes going on in the society. People are saying they want a different texture in their programming."

One executive for a major advertising agency, who spoke only on the condition that he not be identified, agreed. Television, he said, had crossed on occasion into bad taste.

"The mood is different. Now it seems there are people even within the advertising business, people who don't like the pressure groups, who are tending to agree with some of the protests."

Typical of such protests was a Michigan woman's campaign against the Fox Network series "Married . . . With Children." Impressed by her detailed arguments that the program was offensively vulgar and should not have been shown at a time when children could watch it, several advertisers withdrew from sponsoring it.

These factors are cited by industry executives to explain why the issue has has become so inflamed this spring:

-The decision by all three networks last year to cut back staff in their standards and practices divisions, which are responsible for censoring programs, in order to save money.

-The Hollywood writers' strike last spring, which shortened the time between program production and broadcast, and, thus, gave the networks less time to censor potentially offensive material.

-Improvements in technology, including the proliferation of the vid-eocassette recorder, enabling viewers to keep their own recordings of offensive programming and cite specific incidents they find objectionable.

-A spillover onto the networks of a segment of the public's hostility to the more explicit programming offered by "tabloid TV shows," which specialize in often-sensationalized accounts of sex and violence.

-A heightened concern about the vulnerability of children in American society to violence and drugs.

Campaigns to affect program content through appeals to advertisers are not new. In the mid-1970s, such groups as the Parent-Teacher Association and the American Medical Association succeeded in limiting the proliferation of crime shows on the networks by convincing advertisers that the level of violence on television was harmful to children.

In the early 1980s, pressure groups like the American Family Association also attacked television, charging that network programming included explicit sex, profanity and "anti-Christian attitudes."

But the latest effort differs from previous attempts in that the 1970s wave of protests was limited to TV violence, and the religious groups' complaints of the 1980s were largely dismissed as coming from outside mainstream American opinion.

Kathryn C. Montgomery, an assistant professor of Film and Television at University of California at Los Angeles, is the author of "Target: Prime Time," a history of anti-TV campaigns by groups.

She argues that corporate takeovers of all three networks in the past five years created a climate in which a new protest movement could flourish.

"The reason the standards and practices divisions were working in the first place is because they were actively managing the advocacy groups," she said. "Then the ownership changed, the staffs were cut and all that institutional memory was lost. Of course, the advertisers still have that institutional memory."

At the same time, she said, broadcasters took advantage of more freedom allowed by the deregulatory policies of the Reagan administration.

The networks maintain that they have not relaxed their standards. But last month, NBC reinforced its standards and practices division by re-establishing the post of vice president of program standards. Rosalyn Weinman was named to the position.

Terry Rakolta, the Michigan homemaker who campaigned against the Fox Network program "Married . . . With Children," received widespread attention because she impressed advertisers as a person expressing a widely shared view. Tartikoff agreed that parental concerns had helped make the protests a mainstream issue.

"I think parents are concerned about young, impressionable minds," he said. "There are a lot of issues in the society that people are uneasy about. They look at television, see things on the news, drugs, violence, and say we can't have much impact on these issues as we'd like to have. But maybe we can on the programs we see on TV."